This present study of ACEA 1021 is a multi-center, double-blind, centrally-randomized, vehicle-controlled, single dose, rising tolerance design to evaluate the safety, tolerability, and pharmacokinetics of ACEA 1021 in patients with acute stroke. Forty-five patients who fulfill criteria will be treated within 48 hours of onset of stroke symptoms and will be studied in five sequential dosing groups at three to five sites. Each Group will consist of a minimum of nine patients, of whom six will receive the test article, ACEA 1021, and three will receive the vehicle-control, 0.05 M Tromethamine (TRIS). Patients will be evaluated at several time points for safety and tolerability. Each patient will be closely observed and will have continuous monitoring of cardiac rythm during the infusion and for 24 hours after administration is complete, and will have laboratory tests (CBC, Chemistry, and urinalalysis) at 24 hours, 48 hours, one week, and one month post-dosing. Each patient will remain hospitalized during the infusion and for 48 hours after administration of ACEA 1021. Each patient will be seen as an outpatient (if discharged from hospital) at one week and one month post-dose in order to evaluate their clinical status. ACEA 1021 levels will be drawn at baseline, at the end of study drug infusion, at fifteen minute intervals for the first hour post-dose, and at 2, 4, 8, 12, 24, and 48 hours post-dose. Patients will be followed for 30 days. This study represents the first administration of ACEA in humans. ACEA 1021 is a new molecular entity (5-nitro-6, 7-dichloro-2, 3- quinoxalinedione) which acts as an N-methyl-D-asparate (NMDA) antagonist at the Glycine site. It provides neuroprotection in multiple models of cerebral ischemia, both in vitro and in vivo, as well as in vivo models of seizure and pain. It has an approved cardiovascular and CNS safety profile compared with other NMDA antagonists and an acceptable toxicology profile for administration of a single dose in humans. In the preclinical animal studies, risks attributed to ACEA 1021 included CNS effects, liver and renal toxicity, mild anemia, and local irritation at the infusion site. Risks of ACEA 1021 have included PCP- like side effects, vomiting or effects on blood pressure and heart rate. Nevertheless, these parameters will be monitored during the infusion and for 48 hours after infusion is completed. The minimal vacuolization without necrosis of neurons seen with acute administration of 30 mg/kg in rats, and conflicting results in genetotoxicity studies must also be considered in the risk assessment, but cannot be monitored during this study.